These IQTV and SQTV integrated systems are ever more largely employed in video receivers to improve image quality without requiring changes in the relevant transmission standards (PAL, NTSC, SECAM). In practice, luminance (Y) and chrominance-U and chrominance-V (UV) analog components of the video signal are digitized through relevant analog-to-digital converters. The digital data obtained, concerning the two fields into which the video signal is generally divided, are stored in a dedicated memory. This allows, first, a conversion from 50 or 60 Hz to 100 or 120 Hz of the interlaced scanning frequency (in practice the so-called "refresh-rate") so to make flickering imperceptible.
Moreover, digital values relevant to each pixel of each line forming each field so stored in the memory, enable implementation of appropriate algorithms for reducing gaussian and spike or pulse noise. Through memory duplication, it is also possible to implement a compensation (elimination) loop of blurring of objects moving fast on a background, employing an algorithm that contemplates the calculation of average values among the values of pixels relating to successive pictures so to eliminate non-correlated contents of the video signal and correction algorithms based on motion detection.
In general, the field memory or memories are DRAM devices which according to the present limits of manufacturing technologies, are external to the integrated device containing the processing circuits (generally called SQTV.sub.-- IC or IQTV.sub.-- IC). A common video receiver includes a tuning section, that selects the channel and the relevant frequency band of the signal transmitted via cable, satellite, or from ground-based stations. The tuner converts the received signal to an intermediate video frequency (for example 38.9 Mhz according to the Italian standard) containing luminance and chrominance data multiplexed in frequency. A demodulation block processes the signal converted at intermediate frequency, producing a base band composite video signal, which is selected by a selector of the input signal source and feeds the standard decoder (PAL, NTSC, SECAM) carrying out the separation of luminance and chrominance components.
Analog signals relevant to luminance (Y) and chrominance (UV) are thus converted through appropriate analog-to-digital converters so to produce a luminance (Y) digital data stream and a chrominance (UV) digital data stream which are fed to the IQTV.sub.-- IC (or SQTV-IC) device). Each FIELD MEMORY may store a picture field in the 4:2:2 format or in the 4:1:1 format, thus occupying the following memory space
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720 .times. 288 .times. 8 for luma (luminance) (Y) 1,658,880 bits =3,317,760 bits 350 .times. 288 .times. 8 for U chroma (chrominance 829,440 bits 360 .times. 288 .times. 8 for U chroma (chrominance 829,440 bits NTSC 720 .times. 240 .times. 8 for luma (luminance) (Y) 1,382,400 bits =2,764,800 bits 360 .times. 240 .times. 8 for U chroma (chrominance 691,200 bits 360 .times. 240 .times. 8 for chroma (chrominance V) 691,200 bits __________________________________________________________________________
In the case of a PAL transmission system which, being the more critical standard, can be taken as reference example, the total requisite, when employing two field memories becomes 3,317,760*2=6,635,520 bits. There is the need or usefulness to reduce this memory requisite of a SQTV.sub.-- IC (or IQTV.sub.-- IC) without causing a perceivable visual deterioration of images. A reduction in the memory requisite may save costs and/or create more suitable premises for the integration of the field memory in the same IQTV.sub.-- IC (or SQTV.sub.-- IC) chip, through advancements of manufacturing processes.